1. Field of the Invention
This invention relates to an improvement of surfactants available for various products including food and cosmetics. More particularly, it relates to an improvement of various surface activities of surfactants which are widely approved in many countries and highly safe when employed as materials for the production of, e.g., food, cosmetics and pharmaceuticals, i.e., polyglycerol fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters and glycerol fatty acid monoesters.
2. Description of the Prior Art:
Polyglycerol fatty acids esters, which exhibit excellent biodegradabilities and approved to be safe, are widely employed in, for example, food and cosmetics as surfactants having various functions including emulsification, dispersion, solubilization, wetting and foaming, since they can show surface activities of a wide range hydrophile-lipophile balance (HLB) depending on the degree of polymerization and the type and number of the binding fatty acids.
Among these polyglycerol fatty acid esters, however, hydrophilic ones having an HLB of 13 or above would not give so stable emulsion of edible fats and oils as such and are thus unsuitable therefor, although they are soluble per se in acidic aqueous solutions or aqueous solutions of inorganic salts such as common salt. On the other hand, those having an HLB of 9 to 11 and generally used for emulsifying, for example, edible fats and oils and liquid paraffin are unstable to acidic aqueous solutions and aqueous solutions of inorganic salts such as common salt.
Further polyglycerol fatty acid esters having an HLB less than 9 are insoluble in acidic aqueous solutions and aqueous solutions of inorganic salts such as sodium chloride and inavailable in emulsifying edible fats and oils as such.
The wetting, solubilization and dispersion capabilities, which are important properties of surfactants, of polyglycerol fatty acid esters are lower even in the case of hydrophilic ones than other surfactants. For example, the permeation capabilities of the same are lower than those of sucrose fatty acid esters and thus, needless to say, much lower than those of a polyoxyethylene alkylphenol ethers.
Sucrose fatty acid esters, which exhibit excellent biodegradabilities and are approved as safe, are widely employed in, for example, food and cosmetics as surfactants having various functions such as emulsificaiton, dispersion, solubilization, permeation and foaming since they can show surface activities of a wide range of HLB depending on the type and number of the fatty acids bound to sucrose.
However these sucrose fatty acid esters, which are nonionic surfactants, are readily precipitated in acidic aqueous solutions and aqueous solutions of inorganic salts such as common salt, which lowers the surface activities thereof. Although sucrose fatty acid esters containing monoesters in an amount of almost 100%, in particular those which are monoesters of short-chain or unsaturated fatty acids, are relatively stable in acidic aqueous solutions or aqueous solutions of inorganic salts, they are extremely expensive and can not be employed in practice.
Thus most of commercially available sucrose fatty acid esters have a disadvantage that they would almost lose the surface activities at a pH value of 4 to 6 or at a common salt concentration of 1%. There are many aqueous solutions of, for example, food products having pH values or common salt concentrations within the ranges as described above. Therefore the above disadvantage of sucrose fatty acid esters strictly limits the application of the same.
In addition, the permeation capability, i.e., wetting power, which is one of the surface activities, of a sucrose fatty acid ester having a high HLB is insufficient when compared with that of, for example, a polyoxyethylene alkylphenol ether.
Sorbitan fatty acid esters are esters of one or more compounds selected from among sorbitol, sorbitan and sorbide, the latter two being intramolecularly dehydrated products of the former, with a fatty acid. They can exhibit surface activities of a relatively lipophilic HLB depending on the type and number of the binding fatty acids. They are widely used in various products including food and cosmetics as surfactants, mainly as an emulsifiers, which show excellent biodegradabilities and are approved as safe.
However sorbitan fatty acid esters generally show poor solubilities in water. In particular, they are apt to be readily precipitated in acidic aqueous solutions of, for example, a pH value of 5 to 6 or aqueous solutions of inorganic salts such as sodium chloride at a concentration of, for example, 1%, which lowers the surface activities thereof.
There are many aqueous solutions of, for example, food products having pH values or common salt concentrations within the ranges as defined above. Thus the above disadvantage of sorbitan fatty acid esters strictly limits the application of the same.
In addition, the wetting and dispersion capabilities, which are important surface activities, of sorbitan fatty acid esters are very poor.
Glycerol fattly acid monoesters, which are natural surfactants present in living organisms, are produced through transesterification between fats or oils and glycerol or reactions between fatty acids and glycerol. Since these glycerol monoesters have simple structures, they can be readily purified to a high purity by distillation. Thus they are useful surfactants and available at a relatively low price. However the glycerol monoesters are highly lipophilic and insoluble in water. Those containing a large amount of impurities including fatty acid soaps can be dispersed in hot water but would cause phase separation at room temperature, which strictly limits the application of the same.